The present invention relates to an LED driver for powering an LED fixture comprising one or more LEDs and a method of operating an LED assembly comprising an LED driver and an LED fixture.
At present, in architectural and entertainment lighting applications more and more solid state lighting based on Light Emitting Diodes (LED) is used. LEDs or LED fixtures have several advantages over incandescent lighting, such as higher power to light conversion efficiency, faster and more precise lighting intensity and color control. In order to achieve this precise control of intensity and color from very dim to very bright light output, it is necessary to have accurate control of the current as provided to the LED fixture.
In order to provide said current to the LED fixture, an LED driver is applied. In general, an LED driver comprises a power converter or a regulator such as a linear regulator and a control unit for controlling the converter. Examples of such converters are Buck, Boost or Buck-Boost converters, fly-back converters or hysteretic converters. Such converters are also referred to as switch mode current sources. Such current sources in general provide a current comprising a ripple at a comparative high frequency (e.g. 50 kHz to 500 kHz). Depending on the type of converter that is used, said ripple (e.g. characterized by its peak to peak value) can be comparatively small or comparatively large compared to the DC value of the current. The current sources or converters as applied in an LED driver are controlled by a control unit, which can e.g. comprise a microprocessor, controller or the like. In general, the control unit receives, e.g. via a user input device, a input signal (also referred to as a set point) representing a desired output characteristic of the LED fixture. The desired output characteristic can e.g. be a desired brightness or color. As the brightness of an LED strongly depends on the current as provided to the LED, it is important to have an accurate knowledge of the current that is supplied to the LED fixture. In order for the control unit to control the power converter providing the current to the LED fixture, a feedback signal representing an average current value is often generated and provided to the control unit. Know solutions to determine such an average current value often require an extensive calculation time, resulting in an unwanted delay, or require additional hardware, resulting in an increased complexity (and thus costs) of the LED driver.
In view of these drawbacks, it is an object of the present invention to facilitate the determination of a feedback signal representing an average current as provided to an LED fixture.